The invention relates to a liquid meter having a measurement chamber in which a spinner is driven in rotation about an axis and pivots, at least at low liquid flow rates, on a support in alignment with the axis.
Liquid meters of this type are known, e.g. as described in documents GB 437 637 and FR 2 336 666. In those meters, the pivoting motion of the vertical axis spinner is conventionally performed by means of a fine conical tip connected to the support, as in document GB 437 637, or to the axis of the spinner, as described in document FR 2 336 666, and in contact with a plane or concave surface associated with the spinner (GB 437 637) or with the support (FR 2 336 666). Contact between the conical tip and the plane or concave surface is almost point contact and enables mechanical friction to be kept small while the spinner is pivoting on its support, thereby imparting good sensitivity to the liquid meter.
In the water meter described in document FR 2 336 666, provision is made for the spinner to rise when the flow is above a certain rate, thereby separating the conical tip and the plane or concave surface, and thus reducing the risk of the tip being subjected to wear. By moving the conical tip and the surface apart, it is ensured that the point contact does not become an area contact, thereby increasing friction while pivoting.
Nevertheless, it would be advantageous to find a solution to the problem of the conical tip being subject to wear in contact with the plane or concave surface when said contact needs to continue over a long period of time.
The present invention seeks to remedy this problem by proposing a solution that is of simple design and that is very effective.
The present invention thus provides a liquid meter comprising a measurement chamber in which a spinner is caused to rotate about an axis and pivots, at least at low liquid flow rates, on a support in alignment with said axis, wherein pivoting motion takes place via a ball that is free to rotate between two concave surfaces each having a radius of curvature that is greater than the radius of curvature of the ball.
By proposing rolling point contacts between the ball and each of the concave surfaces, it is ensured that it is not always the same points that come into contact over a period of time, and thus that wear of the ball is greatly reduced compared with wear of the prior art conical tip.
Even after the spinner has been pivoting on its support for a long time, point contact is maintained, thereby guaranteeing that the initial sensitivity of the spinner is maintained.
In addition, contact between the ball and the top and bottom concave surfaces ensures that the ball is centered automatically, thereby making it possible to recenter the spinner relative to its support, and thus avoid lateral friction when the spinner is off-center.
By way of example, the axis may be vertical when the meter is disposed horizontally.
According to another characteristic of the invention, the upper limit for the radii of curvature of the concave surfaces is determined by the weight of the spinner in the liquid, with the radii of curvature increasing with increasing weight of the spinner in the liquid.
Automatic centering of the ball depends on the weight of the spinner in the liquid and on the radii of curvature of the concave surfaces.
According to a characteristic, one of the concave surfaces is tied to the spinner whereas the other surface is secured to the support.
By way of example, both concave surfaces are substantially spherical, parabolic, or elliptical in shape.
It is even possible to envisage the shapes of the two surfaces not being both of the same type. Thus, for example, one of the surfaces may be spherical while the other is elliptical. Any such combination can be taken into consideration by the person skilled in the art. For reasons of simplicity, it is preferable to select the same radius of curvature for each of the concave surfaces, but that is not a technical necessity of any kind.
Depending on whether the mean density of the spinner is greater or less than the density of the liquid, the ball is placed beneath the spinner or above it. In either of the two cases envisaged above, an axial housing may be provided in the spinner to receive the support constituted by the ball and by an axial pivot provided at one of its ends penetrating into said housing with one of the concave surfaces for coming into contact with the ball, the other concave surface being formed at the end of said axial housing of the spinner.
As a variant, in either of the cases envisaged above, provision can be made for an axial shaft secured to the spinner to penetrate into an axial housing having one of said concave surfaces formed at the end thereof, said axial shaft being provided at one of its penetrating ends with the other concave surface, the ball being disposed in said housing between said surfaces.